The invention relates to a butt connection between two round, flattened oval, or rectangular air duct sections made of sheet metal.
Numerous different forms of butt connections between individual sections of an air duct are known in air duct construction, in which different flange frames must be used to connect rectangular, round, or flattened oval air ducts, firstly to achieve inexpensive manufacture and assembly, and secondly to achieve sufficient stability and sealing. In addition, a change is under way in the presently used air duct construction, involving an increasing shift from sheet metal ducts that are creased, bent, and folded, to ducts that are wound from sheet metal strips. Starting with the familiar round, so-called wound connection tubes or spiral connection tubes, tubes with a flattened oval cross section were made by spreading these round tubes, and recently there have also been wound rectangular ducts with slightly rounded corners. The wound ducts have numerous advantages such as airtightness without special sealing measures, automatic continuous manufacture, unlimited lengths for the individual air duct sections, with a length of 6 meters being conventional, and consequently a considerable savings in flanges and assembly time. Flattened oval and rectangular cross sections are therefore used preferentially because in most buildings the room height is insufficient for larger round tubes.
On the other hand, wound connection tubes and flattened oval and rectangular ducts made from them pose problems when a flange frame is to be mounted on the end of an air duct section, because of the coiled connection spiraling around the tube. In all wound tubes and ducts, the connection is on the outside because if it were inside it would impede the air flow inside the duct. Wound tubes and ducts therefore have a smooth interior, while ducts made from sheet metal panels are smooth both inside and out. The problem is further increased by the fact that in flattened oval and rectangular wound ducts, and also in round wound connection tubes, a so-called web connection or additional ribs are increasingly being used to reinforce the duct surfaces to reduce the thickness of the sheet metal. This web connection or rib reinforcement is especially necessary in rectangular and flattened oval wound ducts, since in these cases stabilization provided by curvature is absent, which is very helpful in round tubes.
These irregular projections on the outer surfaces of wound ducts and tubes make it impossible to insert the duct wall, as in conventional rectangular ducts, into the opening of a flanged connector mounted on the end of the tube or duct to produce the butt connection. Therefore, it is only possible to use an essentially L-shaped flanged connector with one flange leg projecting essentially radially outward and one flange leg abutting the inside of the tube or duct and fastened to said inner side, and a gasket between the connector and the end of the duct. An embodiment is known for round tubes in which the inner flange leg of the connector is fastened by a spreading edge to the inside of the tube. However, in a flattened oval or rectangular duct, such a fastening of the flange frame no longer functions; instead, the frame must be fastened to the sheet metal duct by spot welding, screwing, or riveting. A seal is then produced by embedding the end of the duct wall in a bead of sealant on the flange frame. These embodiments have the disadvantage that in round tubes, gaps result between the ends of the rounded flange frame and, in flattened oval or rectangular ducts, between the individual sections of the flange frame as a result of the use of intermediate connectors, and these gaps cannot be sealed in this simple fashion. In addition, there is also the disadvantage that an L-shaped flange means cannot withstand the pull of the threaded bolts that pull the two flange frames together to form a butt connection without additional stabilizing devices. None of these known butt connections is suitable for rectangular wound ducts with rounded corners, since a "corner connector" of known design that bridges the rounded corner has a space between the individual flange frame sections which is very long and cannot be sealed, and also could not withstand the pull of the connecting threaded bolts.
In addition, it is important to consider in the case of all of the types of butt connection that have been mentioned that, in the case of the intermediate connectors between the individual flange sections, which jointly form a flange frame, the distance between them which is not sealed is further increased considerably by the fact that the flange frame and must be made several millimeters smaller than the interior of the duct, so that the inner flange leg can be inserted into the interior of the duct and the unavoidable variations in the interior dimensions of the duct can be taken into account. Therefore, when the flange frame is fastened, the intermediate connector is pulled out slightly from the flange frame so that the inner flange leg can fit tightly against the interior of the duct.
The goal of the invention is to produce a butt connection of the type recited at the outset, which is equally usable for round, oval, or rectangular air duct sections and which, despite manufacture of the air duct by the winding method and the therefore necessary connections and possibly reinforcing ribs, a continuous reliable seal of the flange frame including intermediate connectors to the ends of the channel sections is possible.